1. Field of the Invention
This invention relates hoses suitable for hydraulic or high-pressure use and more particularly to such hoses having specified modulus and thickness characteristics.
2. Prior Art
In general, heavy-duty hoses are used to transport or otherwise handle oily fluids at elevated pressure and temperature for prolonged periods of time. Known hoses of this type are constructed with a brass-plated, wired layer of reinforcement or with a multi-layered inner tube having inner and outer peripheral walls formed of different rubbers. A metal coupling joint is usually clamped on both ends of the hose to enable connection with various piping arrangements. Clamping force is intense enough to protect the coupler against loosening or detachment due to pressure being internally exerted by the hose in service.
The foregoing prior hose of a multi-layered structure is prone to develop varying strains under such clamping force because the laminated rubbers are physicallay different. This in turn leads to bursted rubber in the vicinity of a boundary of the rubbers and eventual delamination, given somewhat adhesiveness, and thus results in expanded or sometimes ruptured inner wall at adjacent to the coupler as is commonly termed bulging.
Certain rubber materials have been proposed which are highly resistant to oils and thermally stable at ambient temperatures generally of 120.degree. to 150.degree. C. They include for example acrylonitrile-butadiene copolymer rubber (NBR), acrylic rubber (ACM), ethylene-acrylic copolymer rubber (AEM), ethylene-acrylic-vinyl acetate terpolymer rubber (ER), chlorosulfonated polyethylene rubber (CSM), chlorinated polyethylene rubber (CM) and hydrogenated acrylonitrile-butadiene copolymer rubber (hydrogenated NBR) in which the conjugated dienes are hydrogenated.
Most heat-resistant among the above rubbers is hydrogenated NBR hereunder called H-NBR. However, H-NBR needs to be cured in the presence of an organic peroxide so as to produce that quality in a maximum extent. Peroxide-cured H-NBR, though adequately adhesive to other rubbers so cured, is less bondable to brass-plated wires or organic fibers useful for reinforcement. A wire-reinforced hose, usually exposed to more severe conditions than a fiber-reinforced hose, is susceptible to bursting arising out of insufficient adhesion between the inner rubber tube and the wired layer. Firm bonding of rubbers to wires and also to fibers is a great concern from the hose performance point of view.
A hose of an H-NBR inner tube combined with a brass-plated, wired layer has been found impractical as this rubber is not sufficiently bondable to the wires.
An improved type of hose has been proposed by the present inventors, the hose being comprised of an inner tube including an inner wall and an outer wall, and a reinforcing layer superimposed one on another as disclosed in U.S. Ser. No. 072, 567. The inner wall is formed of peroxide-cured H-NBR, and the reinforcement is made of brass-plated wires. The outer wall disposed for contact with the wires is composed of acrylonitrile-butadiene rubber (NBR), sulfur (S), an organic peroxide (PO) and a 6-R-2,4-dimercapto-1,3,5-triazine (F) as later referred to simply as NBR-S-PO-F. This hose, though quite satisfactory in respect of other important qualities, is liable to bulge when clamped with a coupler.